In lighting systems, usually a master unit controls the operation of attached slave units, for example lamps. A connection between the master unit and the slave units usually uses a directed wired connection, or a bus connection, for example DALI, or even a wireless connection. Implementing a full bidirectional communication between the master unit and the individual slave units requires a receiver and a transmitter on both ends. This results in a complex hardware of the individual components and thereby a high manufacturing cost. A solution to this problem is to reduce the communication to a unidirectional communication from the master unit to the slave units. In this case though, a feedback from the slave units to the master unit is not possible. The master unit has no way of knowing if a command has reached its destination and was implemented.
The German patent application DE 10 2004 002 027 A1 shows a lighting system, in which a master unit provides power to a number of slave units using a DC output circuit. The state of the DC output circuit is monitored. The slave units are able to deliberately change the state of the DC output circuit in order to transmit feedback information to the master unit.
The system shown there though is disadvantages, since the slave units require a communication unit able to affect the state changes of the DC output circuit. In comparison to a full bidirectional communication between the master unit and the slave units, this solution does not significantly reduce the hardware complexity.